This invention relates to a clothes washing machine wherein a drive motor for driving an agitator and a rotational tub is driven at a target number of revolution.
An agitator is provided in a rotational tub serving both as a washing tub and a dehydrating tub, for example, in full automatic clothes washing machines. The agitator is rotated alternately forward and backward by a drive motor in a washing step while the rotational tub and the agitator are rotated by the drive motor in a dehydration step. It has recently been proposed that a brushless motor be employed as the drive motor in the above-described type clothes and that the brushless motor be driven at a target number of revolution by an inverter drive circuit. More specifically, a microcomputer-based control device is provided for controlling various loads of the clothes washing machine based on inputs from switches in accordance with a previously stored operation program. The control device comprises a revolution command section for commanding a target number of revolution to drive the motor at it and a voltage command section for supplying the inverter drive circuit with the voltage applied to the motor based on the command from the revolution command section. A revolution detecting section is also provided for detecting the number of revolution of the motor so that a feedback control is performed based on the detected number of revolution of the motor.
The drive motor needs to be deenergized immediately when locked for the reason, for example, that clothes are caught in between the agitator and the rotational tub during the washing operation. Further, the user needs to be warned against such an abnormal condition. In this case it is generally considered that whether or not the number of revolution of the motor can reach a predetermined value can be determined for the purpose of detecting such a locked motor condition. However, an amount of load applied to the motor is varied because of the position of the clothes in the rotational tub or the like, resulting in unevenness in the number of revolution. Consequently, it is difficult to detect the locked motor condition with reliability or to determine whether the locked motor condition is temporary and safe or continuous and dangerous.
Further, in the feedback control of the motor revolution, the number of revolution detected by the motor speed detecting section is compared with the target number of revolution at that time. The voltage applied to the motor is increased by a predetermined value when the detected number of revolution is smaller than the target number of revolution while the applied voltage is decreased by a predetermined value when the detected number of revolution is larger than the target number of revolution. However, the number of revolution of the motor is sometimes changed suddenly depending upon the position of the clothes in the rotational tub as described above or when the clothes are put into or taken out of the rotational tub during the washing operation. In such a case the conventional feedback control requires much time for the motor to reach the target number of revolution.